The connections service no longer depends directly on the
syncthing model object, but on an interface instead. This
makes it drastically easier to write clients that handle
the model differently, but still want to benefit from
existing and future connections changes in the core.
This was motivated by burkemw3's interest in creating a
FUSE client that can present a view of the global model,
but not have all of the file data locally.
The actual decoupling was done by adding a connections.Model
interface. This interface is effectively an extension of the
protocol.Model interface that also handles connections
alongside the modified service.
The XDR encoder doesn't understart slices of strings very well. It can
encode and decode them, but there's no way to set limits on the length
of the strings themselves (only on the length of the slice), and the
generated diagrams are incorrect. This trivially works around this,
while also documenting what the string actually is (a URL).
This should resolve the spurious ping timeouts we've had on low powered
boxes. Those errors are the result of us requiring a timely Pong
response to our Pings. However this is unnecessarily strict - as long as
we've received *anything* recently, we know the other peer is alive. So
the new mechanism removes the Pong message entirely and separates the
ping check into two routines:
- One that makes sure to send ping periodically, if nothing else has
been sent. This guarantees a message sent every 45-90 seconds.
- One that checks how long it was since we last received a message. If
it's longer than 300 seconds, we trigger an ErrTimeout.
So we're guaranteed to detect a connection failure in 300 + 300/2
seconds (due to how often the check runs) and we may detect it much
sooner if we get an actual error on the ping write (a connection reset
or so).
This is more sluggish than before but I think that's an OK price to pay
for making it actually work out of the box.
This removes the configurability of it, as the timeout on one side is
dependent on the send interval on the other side. Do we still need it
configurable?
